1. Field of the Invention
This invention relates to a device for preventing fuel, e.g. gasoline, from flowing from the vent of an automobile fuel tank. In use, such fuel leakage preventing device is attached to the vent of an automobile fuel tank.
2. Description of the Prior Art
Usually a vent pipe is attached to the gasoline tank of an automobile for venting fuel vapor at a raised pressure from the tank to the atmosphere through an associated canister. It is necessary to provide means for preventing gasoline from flowing from the vent of the gasoline tank because otherwise, gasoline would flow out from the vent of the gasoline tank to disable the canister when the automobile inclines by a large angle while cornering or while stopped on a steep slope.
In a prior art device for preventing gasoline from flowing from the vent of the gasoline tank when the automobile body is inclined, a steel ball rolls down on an inclined surface to the vent of the gasoline tank, thereby closing the vent with the steel ball like a stopper (See U.S. Pat. No. 3,996,951). This device, however, cannot stop the leakage of gasoline when the gasoline splashes in the fuel tank. Such splashing is caused by sloshing of the gasoline in the fuel tank while the automobile is traveling.
In an attempt to overcome such drawback a device has been proposed which comprises a valve compartment fitted in an opening of the ceiling plate of a gasoline tank and a float vertically movable in the valve compartment. In operation, when the automobile body is inclined, the gasoline raises the float until the head projection of the float fits in the vent hole at the center of the ceiling of the valve compartment, thus closing the vent like a stopper (See Japanese Utility Model Application Public Disclosure No. 59(1984)-22373). When the automobile body returns to the horizontal position, the float descends by gravity to open the vent of the gasoline tank. Disadvantageously if the fuel remains in the annular clearance between the outer surface of the float and the inner surface of the valve compartment under the influence of surface tension, the float is caught by the combined effect of the surface tension of the trapped gasoline, the negative pressure applied to the head of the float around the vent of the tank and the positive pressure applied to the bottom of the float in the tank. In this state, the float cannot descend. When the float thus caught is subjected to the vibration transmitted from the running automobile, the fuel remaining in the annular clearance between the valve compartment and the float loses its surface tension intermittently, thereby moving the float up and down as if it were coughing, and allowing gasoline to leak to the canister through the vent of the tank.
As a remedy the annular clearance between the outer circumference of the float and the inner wall of the valve compartment is enlarged. However, the float is liable to move sideways, and this sideway movement causes a reduction in the exactness with which the head of the float fits in the vent hole of the gasoline tank. Also, disadvantageously the size of the valve compartment is enlarged accordingly.